Semi-submersible pumps with mechanical seals
Villina-GNVCP-2T type vertical electric semi-submersible pumping units are designed for transit in stationary conditions of neutral, corrosive, toxic, as well as explosive and fire hazardous liquids, the vapors of which can form explosive mixtures with air. These are used in gas, petrochemical, petroleum refining and other industries.
Main technical specifications
- Temperature of the pumped fluid: -50oС до +420 oС
- Viscosity up to 160 cSt
- Density 2,000 kg/m3 max, with a high concentration of particles
- Particle size over 0.2 mm, but not exceeding free passage of the impeller (3 to 12 mm depending on the pump rate)
For such conditions, mechanical seals of well-known companies such as OOO NPC ANOD, JSC TREM ENGINEERING, UNICHIMTEK Group of Companies and others are used.
The vertical semi-submersible pump – the pump part is fully or partially in the pumped liquid. The unit consists of a pump part, drive sections, a base plate, a device that transmits torque from the drive, an electric motor (drive).
The ground part comprises a console fastened to the base plate, an electric motor mounted and fastened to the console, and a mechanical seal support system fastened to a base plate.
The semi-submersible part comprises drive sections fastened to the base plate, an elastic coupling body connected to the lower drive section, a pump connected to the elastic coupling body and a discharge line.
The drive sections perform the function of transmitting rotation from the electric motor to the pump part of the unit. They include sleeves (drive section housing), section shafts and rolling-element bearings. The number of drive sections depends on the pump submergence. Splined couplings transmit torque from section to section.
The pump consists of a suction and pressure housings with cascades between them which include impellers and guide vanes. The rotor rests on rolling-element bearings which absorb residual axial and radial loads acting on the rotor shaft.
The pumped fluid is separated from the environment by a mechanical seal which is located in the buffer chamber filled with barrier fluid. The chamber contains rolling-element bearings and a barometric mechanical seal, too.
Sealing is achieved by using two polished surfaces, one of which is secured in the body, and the other one is fixed and rotates with the shaft, creating a perpendicular movement by means of centrifugal forces, which prevents leakage.
When such a seal design is used, the barrier fluid pressure is lower than that of the pumped fluid. In the event of a seal failure, the pumped fluid enters the barrier fluid, not vice versa. This can be significant for a number of applications where entry of foreign fluid into the discharge line is unacceptable.
The pressure differential of the medium being sealed, as well as of the barrier fluid, is controlled by the first contour friction couple. The second friction couple (atmospheric) runs under atmospheric and barrier fluid pressure differentials.
The barrier fluid circulation is provided by dynamic impeller mounted on the shaft.
The barrier fluid can be oil, glycol, antifreezing agent and other lubrication liquids that do not interact with the pumped fluid.
For feeding the barrier fluid to the buffer chamber, the units are equipped with a Villina manufactured support system that meets the requirements of API 682 standard.
High performance of the end inserts with a specific medium to be pumped is achieved by means of a correct combination of materials used. In this case, the stationary and rotating faces should possess a number of special properties which allow them to be in close contact and quickly move relative to each other. Perfectly smooth surface and high wear resistance contribute to the necessary properties.
Pump operation is allowed provided that the minimum fluid level in the pumped volume is above the lower impeller.
To prevent failures and accidents at the operational location, we recommend equipping the units with an automatic monitoring and protection system that provides:
- discharge pressure control;
- blocking of an empty pump start;
- motor overload protection;
- temperature control of the engine bearings;
- control of the temperature, level and pressure temperature of the barrier fluid in the mechanical seal support system;
- temperature control of the electric motor winding.
Villina GNVCP-2T pumps with mechanical seals are leakproof, have long service life and are highly repairable.